Migrating from GnomeAbout to GtkAboutDialog

Since version 2.6, GTK+ provides the GtkAboutDialog widget as a replacement for
the GnomeAbout dialog in the libgnomeui library.

GtkAboutDialog supports all features
found in GnomeAbout. The
GtkAboutDialog API is bigger, since it follows
the GTK+ policy to have getters and setters for all widget properties,
but it isn't much more complex than GnomeAbout.

To convert an application that uses GnomeAbout to
GtkAboutDialog, as a first step, replace calls
like